Oscillator-mixer circuit with single triode tube



March 10, 1953 F. o. CHESUS ETAL I 2,631,229

OSCILLATOR-MIXER CIRCUIT WITH SINGLE "mom: TUBE Filed Aug. 5, 1949 "/I g M 925232.-

JOH T. KOLEDA 210 1' T 35 is g g/32 26 B7 W qbw T A; ATTORNEYS Patented Mar. 10, 1953 OSCILLATOR-MIXER CIRCUIT WITH SINGLE TRIODE TUBE Frank 0. Chesus, Bayshore, and John T. Koleda, Islip, N. Y.

Application August 5, 1949, Serial No. 108,733

This invention relates to a circuit for a combined oscillator and mixer utilizing a single vacuum tube, this circuit being particularly adapted for use in frequency modulation and television receivers. The circuit utilized is of such a nature that the single tube may be a triode.

We provide an R. F. input circuit, which may be coupled to a previous R. F. stage, and couple this R. F. input circuit by means of a condenser to the grid of a triode. This triode has in addition an oscillator circuit, the tank circuit of which is also coupled by a condenser to the grid. These two coupling condensers are of a low value to keep the coupling between the input and oscillator circuits to a minimum, so that they may be operated at a relatively low difference or intermediate frequency. The grid of the tube is properly biased so that the two signals impressed thereon will be mixed and a resulting intermediate frequency signal produced, generally in the plate circuit.

We prevent the intermediate frequency signal from feeding back into the input circuit by means of a resonant circuit consisting of an inductance and condenser connected in series between the grid and ground. This circuit offers low impedance to the intermediate frequency and high impedance to other frequencies.

While we can connect the cathode directly to ground, at high frequencies we find it advantageous to connect a condenser between the cathode and ground. This counteracts the lowering of the grid-to-cathode impedance of the tube, which becomes appreciable as the frequency rises, and tends to isolate the input and oscillator circuits.

Our invention makes possible an improved detection of radio frequency signals. We use a single triode, oscillator-mixer, instead of a multielement converter tube or separate mixer and oscillator tubes. This reduction in the number of tube elements reduces the amount of tube noise and therefore improves the signal-to-noise ratio.

Our invention is of particular use in frequency modulation and television receivers. We are able to provide a radio frequency tuner having a single envelope, an amplifier tube and a combined oscillator-mixer tube. This results in a smaller chassis and economy of construction.

Other objects and advantages of our invention will become apparent in the following description and annexed drawings, in which preferred embodiments are shown.

In the drawings:

Fig. 1 is a schematic diagram showing our invention utilizing a Colpitts oscillator circuit.

Fig. 2 is a view similar to Fig. 1, but showing a modification of the circuit thereof.

Fig. 3 is a view similar to Fig. 1, but showing a 2 Claims. (Cl- 250-20) further modification of the circuit thereof; and

Fig. 4 is a schematic diagram showing ourinvention utilizing a Hartley oscillator circuit.

Referring to the drawings indetail; and in particular to Fig. -1, it is seen that a signal is received across input terminals I ll of transformer. 'I'. This signal may be of 'a radio frequency and: may be received from an antenna or from aprior radio frequency stage. I I

The secondary H of transformer T may be tuned by a fixed condenser I2 and may also be inductance-tuned by tuning means I3. Any suitable tuning means may be employed. i j 5 Secondary ii and condenser l2 are connected in parallel, and one sideof the circuitis grounded. The other side of the circuit is connected through coupling condenser M to the grid |6j'of the oscillator-mixer tube.

This oscillator-mixer tube is placed in an envelope E, which may also contain one or more other tube units, such as a radio frequency amplifier tube, which are used in different circuits from the one here shown. The oscillator-mixer tube is preferably a triode and has a cathode l5 and plate I1.

In addition to the grid input circuit heretofore described, grid I6 is connectedto ground by means of grid resistor I8.

The oscillator circuit shown in Fig. 1 is of the Colpitts type and makes use of the tube capacities. Optionally, any suitable oscillator circuits may be used, and our invention is not limited to the oscillator circuits herein described.

The tube capacities include grid-to-cathode capacity i9 and plate-to-cathode capacity 29, which are shown in broken lines. These capacities l9 and 20, together with coil 2| and condenser-.22, comprise the tank circuit of the oscillator. One end of coil 2| is connected to plate-I1, and the other end of coil 2| is coupled through condenser 23 to grid "5, and through primary 24 of the intermediate frequency transformer to the B+ plate voltage supply. The lowerend of primary 24 is connected to ground through condenser 26.

The oscillator'grid bias is provided by resistor l8. Coil 2| is tuned by tuning means |3a, which is preferably of the same type as tuning means -|3 and ganged therewith so that the oscillator frequency will vary with the input signal frequency to produce the proper intermediate frequency over the entire band.

When the circuit is in operation, an input radio frequency signal is fed to terminals ID of transformer T and thence to the tuned circuit ll, |2. From this tuned circuit ll, I2 the input signal goes through condenser M to grid Hi.

Simultaneously, the tube generates a signalin oscillator tank circuit I9, 20, 2|, 22, which is preferably slightly higher in frequency than the frequency of the input signal. The difference between the two frequencies is constant over the bandfiiid 'i s'ftli'f desired intermediate free quency. This oscillator signal remains in tank circuit [9, 20, 2|, 22, because the path to ground through transformer 24 and condenser 26 offers high impedance to radio frequencies, a

The two signals impressed'on grid were cone ventionally mixed, resistor 18 being of such'a' value that grid I 6 is biased appioiima'tely to cut-off to give the desired plate rectification.

As a result of the mixing, the difference or,

capacity I9 has little effecton the input circuit,

at high frequencies capacity, l9 offersrelatively little impedance; As aresult, less ofthe signal voltage'idrop occurs "across'condenser I4, which is'iindesirablei" Whn'i'cond'enser 3| is. added, as in Figg, capacities l4, l9 and 31 are in series with the generator ll,"l2; andmost of the voltage drop takes place outside the tube. 7 v

In addition, condenser 31 reduces the coupling be :"een the" input and oscillator circuits, in tfie'einbfodiment'offlFig. 1'; the input circuit has one'side"coupl'ed to grid l6 and the other side grounded; and the oscillator circuithas one side a'lsdco'upledto "grid IBand the other'side connect'd'to' ground through capacity J9, At high frequencies, the impedance of capacity {51 be; comes "too 16w; and the "coupling between the inpu' arido'scillator circuits is too high for them ate" at the proper difierence frequency. Iiith embodiment of Fig. 2, the oscillatorcircuit is connected to' ground through capacity {sf and capacity 3|; which together oifer relativ'ly higli'i'm'pedance to radio'fre'quencies, theretyreauc ng the'cobpling between the input and oscillator circuits. i A

f A further modification of'the circuit, shown in Fig. 3, "is'ajresonant circuit to prevent any intermiuiste frequency signal from being fed back tl'i ohdens''r-Z3 t'o' the" input circuit. ,This 't"circuit"comprises inductance 3.3,, and '6 er 34;"which areconnected in series. between grid"l"and"grbund. The values of in;- dut'ahe '33 and condenser 34 are sucli'that the (ire t'ofirs"very low impedance to'th'e intermii'iat'e frequency but high impedance to the radio frequencies employed. ,Qptionally, any other -suitable circuit may be employed between grfddfiand ground which offers high impedance to radio frequencies but low impedance to the intermediate frequency. 7, f FfifgA is simila'r to Fig. 3,'except that a Hartley dscillatoris'used'instead of a Colpitts oscillator. 'I'h''tank'coil35is tapped at 35, andthis tap 3'6 is connected toground through condenser 31. The principle foperation of the circuit is the -safne as that of the circuit ofv Fig. 3.

Asoneexampk 9f t e ,u e f s fiit. a itable tube which we employ isa "1 2iA"I'7,"in

which capacities l9 and are respectively about 2.5 and 0A5 micro-microfarads. The coupling condensers l6 and 23 respectively are given values of about 12 and 13 micro-microfarads.

Condenser 3| may be 12 micro-microfarads, and inductance 312 may be of any value such that the',cathode circuit is resonant at a frequency different from that of the radio frequencies at which-the ci cu t s 99 In the intermediate frequency series resonant circuit, condenser 34 may have a value of 15 micro' mi'crofarads, and in that case inductance 33 should have a value such that its reactance is equal to the reactance of condenser 34 at or near the intermediate frequency.

In 'all embodiments, we prefer to "employ ppnufri'tunedpnmary; However, pt 0 may be. e l yed,- O e inpu rcuit a bl i used.

What is claimed is: a t W .1!} frequency converter system coinprisingan electron discharge tube having at nest prim: ode, an anode and an inputfgri'd, a source ofinpiit signal connected to said gridand 'cq 'cft ed in serie with a first condenser-to saidcatlidde, "a tuned circuit which comprises a second cbn denser and a coil connected in paralle1, 'on' of the connections between saidfsecond c ndensates said coil being connected to said anode, the other of the connections between said second condenser nd a v @0 1 being en ecte inu er i h third condenser and. said grid, said tubeand said t n d ci cu t ge h ctin s a purts of. loel oscillations which are impressed between said grid and said cathode, and means for deriving frorn the anode to cathode circuit of said tube the sum or'difierence frequency-between=said signal and locally produced oscillations; j,

2. A frequency; convertersystem iii-accordance with clairn l'fin which said jinput signal source is bypassed byga circuitwhich is resonant to saidsum or difference frequency2 FRANK JOHN T. 'KQLEDAL' REFERENCES anti) The following references are of record in'tlie file of this patent:

UNITED STATES PATENT 

